Introduction
The history of cannabis in New Zealand is characterized by a distinct transition from a widely used illicit substance associated with public health risks to a regulated pharmaceutical product. This evolution is anchored by two of the world’s most significant longitudinal studies—the Dunedin Multidisciplinary Health and Development Study and the Christchurch Health and Development Study (CHDS)—which have provided decades of data on the long-term effects of use.
In recent years, the legislative landscape has shifted dramatically. Following the passage of the Misuse of Drugs (Medicinal Cannabis) Amendment Act 2018 and the implementation of the Medicinal Cannabis Scheme (MCS) in 2020, New Zealand has moved toward a medicalized model. This review synthesizes the available literature regarding this transition, organizing findings chronologically from the foundational epidemiological research of the 1970s–2000s to the contemporary regulatory environment of 2020–2024. It addresses regional variations where data permits and highlights the tension between clinical evidence and patient access.
The Epidemiological Foundation (1970s–2010s)
New Zealand’s contribution to global cannabis research is defined by its birth cohort studies, which tracked individuals born in the early 1970s. These studies established the baseline for understanding the health burden of cannabis before the modern medicinal era.
Neuropsychological and Mental Health Outcomes
The Dunedin Study (birth cohort 1972–1973) provides robust evidence regarding the “psyche” component of cannabis impact.
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Cognitive Decline: Persistent cannabis use was associated with global neuropsychological decline. Individuals with three or more diagnoses of cannabis dependence between ages 18 and 38 showed an average decline of 8 IQ points from their childhood baseline. This decline was concentrated among adolescent-onset users and was not fully restored by cessation in adulthood.
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Psychosis and Gene-Environment Interactions: The risk of developing psychotic disorders was found to be conditional. Early cannabis use (by age 15) increased the risk of schizophreniform disorder by age 26 (Odds Ratio 11.38) compared to non-users, even after controlling for childhood psychotic symptoms. Further research indicated this risk is modulated by genetic vulnerability, specifically the COMT genotype, demonstrating a clear gene-environment (GxE) interaction.
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Mental Health Comorbidity: By age 45, 86% of the Dunedin cohort met criteria for at least one mental disorder. Cannabis dependence in this cohort was rarely an isolated event; it frequently co-occurred with other externalizing and internalizing disorders, contributing to a general factor of psychopathology (the “p-factor”).
Physical Health and Epigenetics
Research also addressed the “soma” or physical consequences of long-term use.
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Respiratory Health: A case-control study conducted across eight New Zealand District Health Boards (DHBs) found a dose-response relationship for lung cancer. The risk increased by 8% (95% CI 2–15) for each “joint-year” of cannabis smoking, after adjusting for tobacco use.
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Oral Health: Cannabis use was identified as a risk factor for periodontal disease, independent of tobacco use, within the Dunedin cohort.
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Epigenetic Modifications: In the Christchurch cohort (CHDS), heavy cannabis users were analyzed for DNA methylation changes. While cannabis-only users showed nominal changes in genes related to glutamatergic synapses (P < 0.001), they did not exhibit the distinct epigenome-wide signatures seen in tobacco users (such as changes in the AHRR gene).
Prevalence and Public Health Burden
By the time the cohort members reached their 40s, approximately 80% of New Zealanders born in the 1970s reported using cannabis at least once. While the majority (90–95%) avoided long-term harm, a high-risk minority (5–10%) experienced significant dependence and health consequences. This aligns with global burden of disease data, which identifies cannabis use disorders as a significant contributor to Years Lived with Disability (YLDs) in the Australasian region32154-2),.
The Transitional Era: Barriers and Patient Reality (2010s–2019)
Prior to the full implementation of the Medicinal Cannabis Scheme, patient access was restricted, creating a disconnect between legal frameworks and patient behavior.
The “Substitution Effect” and Illicit Use
Before the 2020 regulations took full effect, patients frequently utilized illicit cannabis to manage chronic conditions. A study of endometriosis patients in New Zealand found that 88.2% self-administered cannabis illicitly, while only 5.9% accessed it via legal prescription. Notably, 0% of respondents reported “legally self-administering” at the time, reflecting the strictness of early regulations.
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Pharmaceutical Reduction: A strong “substitution effect” was observed, with 66.1% of users reducing opioid consumption and 63.1% reducing non-opioid analgesics.
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Barriers: Cost and perceived physician unwillingness were cited as primary barriers. 23.5% of patients did not disclose use to their doctors due to fear of stigma.
Clinical Reluctance and the Evidence Gap
The reluctance of General Practitioners (GPs) to prescribe has been a consistent theme across the Trans-Tasman region.
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Australian Benchmark (2017): In a comparable Australian context, 86% of GPs reported “poor perceived knowledge” regarding medicinal cannabis, despite 61.5% receiving patient enquiries.
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New Zealand Context: New Zealand physicians reported similar barriers, citing a lack of robust clinical evidence (RCTs) as the principal reason for not prescribing. This created an “evidence paradox” where physicians demanded pharmaceutical-grade evidence for a plant-based product, while patients sought relief based on anecdotal or observational success.
The Modern Era: The Medicinal Cannabis Scheme (2020–2024)
The implementation of the Medicinal Cannabis Scheme (MCS) in April 2020 marked a pivotal shift in New Zealand’s approach, aiming to improve access to quality-assured products.
Supply Explosion and Product Shifts
Administrative data from 2020 to 2024 reveals a rapid expansion of the legal market.
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Volume: The quarterly supply of medicinal cannabis products increased 14-fold, rising from 4,827 packs in Q2 2020 to 73,725 packs in Q2 2024.
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The Shift to Flower: Initially dominated by CBD oils, the market shifted significantly in 2023. By early 2024, dried cannabis flower accounted for 40% of prescriptions. This mirrors trends in Australia, where flower products have also seen an upward trajectory in psychiatric prescribing.
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Price Parity: The price of legal dried flower dropped to NZ$11–15 per gram, becoming comparable to the illegal market average of NZ$12 per gram.
The Rise of Specialized Clinics
A defining feature of the New Zealand system has been the emergence of specialized private cannabis clinics. These clinics have filled the gap left by reluctant GPs, becoming the primary access point for many patients. This “privatization” of prescribing has facilitated access but raises equity concerns.
Regional and Demographic Inequities
Despite the explosion in supply, access remains uneven.
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Māori Under-prescribing: Māori received only 12.9% of prescriptions in the analyzed period, despite having higher prevalence rates of cannabis use.
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Regional Data: While specific cultivation and prevalence data for regions like Northland and the East Coast are absent in the reviewed literature, the lung cancer case-control study utilized a sampling frame across eight DHBs, suggesting that health risks are distributed nationally. However, the current literature lacks granular data on how the Medicinal Cannabis Scheme is functioning specifically in rural versus urban DHBs.
Integration and Emerging Patterns
The “Proxy” of High-THC Flower:
The shift toward high-THC flower products (now 62% of verified products are THC-dominant) suggests that the medical pathway may be functioning as a proxy for legal access for some users. This blurs the boundary between “medical” and “recreational” use, a trend also observed in Australia where anxiety and sleep disorders drive the majority of prescriptions.
The Evidence-Practice Gap:
There remains a fundamental tension between the “gold standard” evidence required by traditional GPs and the real-world evidence accepted by specialized clinics. While GPs in 2017/2018 felt unequipped to prescribe, the market has bypassed them through private clinics, leading to a 14-fold increase in supply without a corresponding increase in large-scale clinical trials.
Comparison of Regulatory Models:
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Feature
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New Zealand (MCS)
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Australia (SAS-B)
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Access Pathway
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Specialized Clinics / Section 29
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TGA SAS-B / Authorised Prescribers
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Product Trends
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Shift to Flower (40% of scripts)
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Shift to Flower (31.2% of psych approvals)
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GP Engagement
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Low (Reluctance/Stigma)
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Low (Knowledge Gap)
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Primary Indications
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Pain, Anxiety (inferred from supply)
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Anxiety (66.7%), Pain
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Notes:
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New Zealand data on specific indications is limited compared to the detailed TGA approval data available for Australia.
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Section 29 refers to the provision of unapproved medicines, a key mechanism in the NZ framework.
Gaps and Limitations
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Regional Specificity: The reviewed literature does not contain specific prevalence, cultivation, or prescribing data for the Northland or East Coast regions. While the lung cancer study covered eight DHBs, modern administrative data has not yet been broken down by DHB to show regional uptake of the Scheme.
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Clinical Outcomes: There is a lack of data on clinical outcomes for patients accessing the Scheme. We know what is being prescribed (flower, high THC) but not how effective it is for specific NZ patients compared to the illicit market.
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Māori Health Data: While under-prescribing is documented, there is limited qualitative research exploring the specific barriers (cultural, financial, or geographic) preventing Māori from accessing the legal scheme.
Conclusions
The history of cannabis in New Zealand has evolved from a public health concern focused on the developmental risks of adolescent use to a regulated medical industry. The Dunedin and Christchurch studies established a clear risk profile for early-onset, persistent use, including cognitive decline and psychosis. However, the modern era (2020–2024) is defined by a rapid medicalization driven by patient demand and specialized clinics rather than traditional general practice.
The implementation of the Medicinal Cannabis Scheme has successfully lowered prices to match the illicit market and increased supply by 14-fold. Yet, the system exhibits significant inequities, particularly for Māori, and relies heavily on high-THC flower products that blur the line between therapeutic use and legal access workarounds. While the legislative framework has matured, the integration of medicinal cannabis into standard primary care remains incomplete, stalled by an “evidence paradox” that private clinics have effectively circumvented.